Constant thirst: what this symptom may indicate

Constant thirst is when a person wants to drink more often than usual, and this desire arises regardless of physical activity, air temperature, food salinity and other external factors.

Ordinary thirst itself is a normal response of the body to a violation of water-salt homeostasis, because water plays a vital life-supporting role and is involved in almost all metabolic processes. But if there is constant unquenchable thirst (polydipsia), then it is necessary to understand the causes of this abnormal condition.

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Causes of constant thirst

Domestic medicine considers the physiological norm of water consumption (not in the summer heat) to be approximately 40 ml per kilogram of body weight. The optimal volume of drinking is often mentioned - 1.2-1.5 liters per day. According to the recommendations of the Institute of Medicine (USA), men need almost 3.7 liters of water per day (20-25% - from food, including drinks), women - a liter less. WHO has developed other standards: for men - 2.9 liters, for women - 2.2 liters. In general, to date, as you can see, no consensus has been developed.

The signal about the need to replenish water reserves in the body comes from the so-called drinking center of the central nervous system, which includes the nuclei of the posterior lobe of the hypothalamus, the limbic region of the cerebral hemispheres and certain areas of their cortex. And most often, the causes of constant thirst are rooted in malfunctions of this center.

Thanks to the hypothalamus receptors, the drinking center perceives all fluctuations in the amount, osmotic pressure and level of Na+ in the fluid of all the body structures and responds to them. These reactions are reflexive and involve the neurohormones of the renin-angiotensin-aldosterone system: vasopressin (synthesized by the hypothalamus), angiotensin (formed in the blood), renin (produced by the kidneys) and the adrenal cortex hormone aldosterone. This process is influenced by thyroid hormones, as well as insulin produced by the pancreas.

It should be borne in mind that constant increased fluid consumption is not classified as a disease: in medicine, constant thirst is considered a symptom of a disease.

In many cases, the causes of constant thirst are associated with such diseases and pathological processes as: chronic diarrhea; frequent vomiting; fever; head injuries; infectious intoxication; decreased blood volume (with internal bleeding or systemic capillary leak syndrome); diabetes mellitus (hyperglycemia); diabetes insipidus (insulin-independent) of neurogenic, nephrogenic or dipsogenic etiology.

Thus, constant thirst and frequent urination (polyuria), characteristic of diabetes insipidus, may be associated with:

• with various etiologies of hypothalamic lesions (including tumors), which lead to a disruption in the synthesis of the antidiuretic hormone vasopressin, which regulates water-electrolyte balance;
• with a decrease in osmolality (the concentration of anions, cations and non-electrolytes) of blood plasma;

With low sensitivity (or its complete absence) of renal tubular receptors to vasopressin.

Pathological thirst is also included in the complex of clinical symptoms:

• chronic renal failure (nephropathy, pyelonephritis, amyloidosis, etc.);
• thyrotoxicosis (hyperparathyroidism);
• primary hyperaldosteronism or Conn's syndrome (caused by hyperplasia of the adrenal cortex and increased production of aldosterone, leads to a deficiency of potassium ions - hypokalemia);
• hypohydration in case of edema;
• hyperhidrosis (excessive sweating);
• hypercalcemia;
• hyponatremia;
• hypercortisolism syndrome (Itsenko-Cushing syndrome);
• adrenal adenomas and adrenocortical cancer.

Constant unquenchable thirst and polyuria are observed in congenital genetic pathologies: acromegaly (which occurs when the anterior pituitary gland is dysfunctional), aceruloplasminemia, Bartter syndrome (decreased absorption of chlorides and sodium by the kidneys), cystinosis, Parhon syndrome, Fanconi syndrome, sickle cell anemia.

Persistent dry mouth and thirst accompany the use of certain medications, in particular, all diuretics, most antibiotics, and lithium-containing antipsychotic (neuroleptic) drugs.

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Constant thirst during pregnancy

European doctors claim that during pregnancy women need to drink more during the day – almost 300 ml, but the total volume of liquid consumed should not exceed two liters.

But there is constant thirst during pregnancy (especially at 27-36 weeks), which is explained by an increase in the synthesis of the protein angiotensinogen in the liver and, accordingly, an increase in its entry into the bloodstream. During gestation, this is caused by an increase in the production of corticosteroids and estrogen, a change in the mineral balance.

In addition, as the fetus develops intrauterinely, there is a need to accelerate the glomerular filtration of the kidneys, which work with increased load during pregnancy. And this is facilitated by the high level of angiotensin, which causes increased thirst in expectant mothers.

The biomechanics of homeostatic processes during pregnancy is associated with the fact that angiotensin in increased quantities promotes the growth of the synthesis of the already mentioned aldosterone - a hormone of the adrenal cortex, which leads to the loss of potassium ions in the blood plasma and the retention of excess sodium ions.

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Constant thirst in a child

Let's start, again, with water consumption standards. The World Health Organization's recommendations regarding drinking regimen in childhood are based on the child's body weight: a three-month-old baby weighing up to 5 kg needs at least 700-800 ml of liquid per day,

A one-year-old child weighing 10 kg needs 1 liter of water. Breast milk is included in this standard, as it contains more than 86% water.

According to recommendations from American pediatricians, a child aged one to three years normally consumes about 1.3 liters of liquid per day, including about 350 ml of milk, as well as water, soups, fresh juices and other drinks. From 4 to 8 years old, 1.7 liters per day is needed.

At the age of 9-13, boys need 2.4 liters of liquid per day (European experts cite a different figure - 1.6 liters). And at the age of 14-18, teenagers and young men need 1.9 liters of liquid per day, girls and young women - at least 1.6 liters (the American standard is 2.7 liters and 2.4 liters, respectively).

If a child is constantly thirsty, its causes may be related to one or more of the above factors. To determine the specific etiology, the child needs to be examined: perhaps the child is simply very active, and this increases water consumption to maintain normal water-salt balance. But pathologies are not excluded - both metabolic and neurohumoral in nature.

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Diagnosis of constant thirst

Correct diagnosis of constant thirst, that is, identifying the specific reasons for its appearance, involves collecting a detailed anamnesis, in which the doctor must take into account all the features of the patient's health - from the number of urinations during the day to the features of his usual diet.

Patients are required to submit:

• blood test for plasma glucose content (including fasting);
• blood test for levels of potassium, calcium and sodium (osmotic concentration);
• biochemical blood test;
• general urine analysis;
• urine analysis for relative density.

Based on the test results, the patient may need a consultation with an endocrinologist, hematologist, nephrologist, as well as a CT or MRI of the brain, kidneys, and adrenal glands.

How to quench constant thirst?

To know how to quench constant thirst, it is necessary to determine the optimal volume of water consumed to maintain fluid balance. Considering that water-salt metabolism can have individual characteristics, the need to replenish fluid reserves in the body can vary significantly among different people and depends on their gender and age, mental state and level of physical activity, climatic conditions of the place of residence.

Remember that no sweetened carbonated drinks or beer quench your thirst. Doctors also do not recommend drinking mineral water containing various salts. Very cold water does not help either, since the body absorbs liquids best at a temperature of +22-25°C.

What can be done to prevent constant thirst? By refusing to eat spicy, salty and fatty foods. It is necessary to eat more foods rich in water – vegetables and fruits. Nutritionists consider cucumbers, apples, oranges, melons, and watermelons to be “water-supplying”. Unsweetened green tea at room temperature, apple peel decoction, water with fresh lemon or grapefruit juice added are very good at relieving the feeling of constant thirst. You can also rinse your mouth with cool water.